Gold as hydrogen. an experimental and theoretical study of the structures and bonding in disilicon gold clusters Si2Aun- and Si2Aun (n=2 and 4) and comparisons to Si2H2 and Si2H4

In a previous communication, we showed that a single Au atom behaves like H in its bonding to Si in a series of Si-Au clusters, SiAun (n = 2-4) (Kiran et al. Angew. Chem., Int. Ed. 2004, 43, 2125). In this article, we show that the H analogy of Au is more general. We find that the chemical bonding and potential energy surfaces of two disilicon Au clusters, Si2Au2 and Si2Au4, are analogous to Si2H2 and Si2H4, respectively. Photoelectron spectroscopy and ab initio calculations are used to investigate the geometrical and electronic structures of Si2Au2-, Si2Au4-, and their neutral species. The most stable structures for both Si2Au2 and Si2Au2- are found to be C-2v, in which each Au bridges the two Si atoms. For Si2Au4-, two nearly degenerate dibridged structures in a cis (C-2h) and a trans (C-2v) configuration are found to be the most stable isomers. However, in the neural potential energy surface of Si2Au4, a monobridged isomer is the global minimum. The ground-state structures of Si2Au2- and Si2Au4- are confirmed by comparing the computed vertical detachment energies with the experimental data. The various stable isomers found for Si2Au2 and Si2Au4 are similar to those known for Si2H2 and Si2H4, respectively. Geometrical and electronic structure comparisons with the corresponding silicon hydrides are made to further establish the isolobal analogy between a gold atom and a hydrogen atom.